1. Field Of The Invention
The present invention generally relates to a pulse wave detecting apparatus and particularly to such an apparatus which has a pulse wave sensor including a plurality of pressure sensing elements.
2. Related Art Statement
There is known a pulse wave detecting apparatus of a type which includes (a) a pulse wave sensor having a press surface on which a plurality of pressure sensing elements are provided in an array, the pulse wave sensor being adapted to be pressed at the press surface against a body surface of a subject such that the array of pressure sensing elements crosses over a blood vessel underlying the body surface, each of the pressure sensing elements generating an electric signal representative of a pulse wave transmitted thereto from the blood vessel via the body surface; and (b) a main device receiving the electric signal from the each of the pressure sensing elements In this apparatus, the main device comprises a microcomputer including a central processing unit (CPU). The CPU processes the electric signals, i.e., pulse wave signals supplied from the pressure sensing elements. Based on the shape of a curve representative of a distribution of magnitudes or voltages of the pulse wave signals as taken along the direction of the array of pressure sensing elements, the CPU determines an optimum pressing force to press the pulse wave sensor against the body surface or blood vessel, at which force the blood vessel is deformed to be partially flat, and determines an optimum pressure sensing element, i.e., middle one of the pressure sensing elements positioned directly above the width or lumen of the blood vessel being partially flat, which element generates an optimum or most accurate pulse wave signal. An example of this apparatus is disclosed in the Publication No. 64-12505 of unexamined Japanese Utility Model Application filed by the Assignee of the present U.S. patent application.
In the above indicated apparatus, the array of pressure sensing elements is required to have a sufficiently larger length (i.e., distance between the two elements at the opposite ends of the array) than the width of blood vessel, because it would otherwise be so difficult to locate the pulse wave sensor or array of pressure sensing elements in position with respect to the blood vessel. In addition, the array of pressure sensing elements is required to have the smallest possible space between each pair of adjacent elements and thereby improve the resolution of the pulse wave sensor, for the purpose of accurately determining the optimum pressing force to be applied to the pulse wave sensor and/or determining the optimum pressure sensing element from which the optimum pulse wave signal is produced, and additionally for the purpose of eliminating the cases in which the optimum pressure sensing element determined is not a middle one of the pressure sensing elements positioned directly above the blood vessel.
However, the longer the array of pressure sensing elements becomes and/or the smaller the space between the pairs of adjacent pressure sensing elements becomes, the greater number of pressure sensing elements are needed, and the greater number of pulse wave signals are transmitted to the main device. Consequently, a transmission system which couples the pressure sensing elements to the main device to transmit the pulse wave signals therebetween, suffers from increased amount of burden. In addition, the main device suffers from dealing with an increased number of pulse wave signals.